The positively charged cations in hard water bind with the negatively charged glyphosate molecules, resulting in less-effective weed control.
Don't Let Hard Water Make Weeds Hard To Control - USGA www.usga.org/content/usga/home-page/course-care/regional-updates/central-region/2018/don-t-let-hard-water-make-weeds-hard-to-control.html
www.usga.org/content/usga/home-page/course-care/regional-updates/central-re…
How much? Needs more personal research...
That would make sense. (Trying to drag back up my old college chemistry classes!)
I wonder how rainwater (naturally soft) may react with glyphosate?
Other info.: http://npic.orst.edu/factsheets/archive/glyphotech.html#:~:text=6-,Water,few%20days%20to%2091%20days.
“I wonder how rainwater (naturally soft) may react with glyphosate?”
(My initial web search did not turn up much.)